The reflective optical sensor module emits light and measures the amount of reflected light from an object. The optical sensor module converts electrical current into light, which is directed onto the surface of an object, and converts the reflected light into electrical signals. The incident light can then be reflected by the object, absorbed by the object, or scattered by the object. A portion of reflected and scattered light can reach a photodetector of the optical sensor module; the received reflected and scattered light produces a corresponding signal. The corresponding signal portion is described as “the signal portion” when calculating a signal to noise ratio (SNR). The signal portion may be attenuated due to a loss of a portion of emitted light, which is either absorbed by the object or escaping from being detected by a photodetector. The noise portion mainly comes from the emitted light directly detected by a photodetector and ambient light detected by the photodetector. Due to the poor light guide efficiency, both incident light leakage and stray light disturbance decrease the SNR, and therefore lead to inaccuracy of the optical sensor module.